A number of studies have shown that penetration of the gingival crevicular epithelium is achieved by various compounds, but since these investiations were not quantitative, little could be learned about the dynamics of transport of material through this tissue. It is our objective to gain such knowledge by quantitatively studying the transport of a number of various size molecules, both native and foreign, through intact and non-intact crevicular epithelium. The isolated labial gingival crevice of the incisors of rabbits will be used in these studies. Known concentrations of radioactive compounds will be incubated within the confines of the gingival crevice. Transport will be determined by assaying for the amount of radioactivity present in tissues obtained by biopsy of the gingiva and in serum samples. Our long term goal in this investigation will be to use this model system to study methods by which materials might be inhibited in their passage from the gingival crevice through the epithelial barrier. Since periodontal disease appears to be implicated with the penetration of toxic substances through the crevicular barrier into the underlying connective tissues, it may be possible to find an inhibitor of transport or create a surface barrier over the crevicular epithelium. These studies will thus serve to establish a method for assaying transport through this tissue and will then use this system to explore a new avenue of approach to the prevention of periodontal disease.